We are woefully ignorant of which host cells are educated in the tumor and contribute to distal sites. Further, although it is very likely that specific immune cells (e.g. myeloid) travel to the distal lymph nodes, key features (their identity lifespan, self-renewal, specific functions) of such cells remains unaddressed. Remarkably, we cannot currently know which host cells in a metastatic site first arrived following residence in a primary tumor. In this application we will develop new technologies to lineage-track cells from one organ to all others, over the entire lifespan of the cell and its progeny. We will use this to test the hypothesis that immune cells, particularly those of the myeloid lineage, are 'educated' in the tumor microenvironment and contribute to the composition of distant sites such as lymph node, spleen and possibly metastatic sites; furthermore we will determine the functional consequences of such a contribution. Notably, this will represent the first direct and unambigious demonstration of which cells traffic to and present antigens in draining lymph nodes, a site-to-site mapping of entire lineages, a discovery of novel lineages that traffic out of tumors and a test that metastatic sites contain immune cells that were once within another lesion. This technology solves a major deficit with existing photoswitchable approaches and broadly extends cutting edge live-imaging approaches towards lineage tracing.